Photophysical Study on the Effect of the External Potential on NiO-Based Photocathodes

In present study we investigate the effect of the external potential on a dye-sensitized NiO photocathode on the light-induced charge carrier dynamics by time-resolved photoluminescence and femtosecond transient absorption spectroscopy under operating conditions. Instead of the anticipated acceleration of photoinduced hole injection from dye into NiO at more negative applied potential, we observe that both hole injection and charge recombination are slowed down. We assign this effect to a variation in OH- ion concentration in the inner Helmholtz plane (IHP) of the electrochemical double layer with applied potential, showing that ion adsorption and desorption onto the NiO surface play an essential role as a relay in light-induced charge transfer and recombination. Our work highlights the key role of ions at the electrode surface and in the electrolyte in the realization of efficient solar to fuel devices.